In general, a field emission display (FED) is based on electron emission in a vacuum. That is, a FED plays a role of display equipment by making electrons impact to anode electrodes coated with florescent substance to emit light, after electrons being emitted from electron emission source which is affected by strong electric field produced by impressing thousands of voltages to anode electrode and applying tens of positive voltages to electron emission source from gate electrode. Nowadays, many researches are being made on a FED as a flat panel display of next generation since the FED has excellent brightness and resolution, together with advantages in its light and thin traits.
Silicon tips or metal tips such as molybdenum and so on are mainly used as the electron emission source of said FED. However, metal tips have problems in that operating voltage of them is very high and leakage current is large due to thermal degradation of the tips resulting from their emitting high currents, and as a result, reliabilities and performances of the elements fall down.
In order to solve the above problems, carbon nano-tubes (“CNT”) having superior mechanical and electron emission characteristics as well as electric selectivity, are used as electron emission sources. Carbon nano-tubes are applied to various electric and electronic fields since a carbon nano-tube is a carbon allotrope composed of carbon atoms to constitute a tube form by combining a carbon atom with the other carbon atoms in hexagonal honeycomb pattern.
However, the FED using said electron field emitters has problems in that mutual interferences between pixels are occurred and efficiency of electron emission falls down due to the lack of technologies by which carbon nano-tubes can be formed at the desired locations and arrayed vertically. The emitters for FED which were mainly used in the early developmental stage of said FED had defects in that manufacturing process and structures of them were complicated. Moreover, since the ion beam of high price was needed to use semi-conductors and metals as electron emission sources, there was another problem that they could not be applied to the FED.
Further, a conventional FED had spacers installed between anode and cathode substrates to maintain a vacuum gap with a predetermined width ranging from tens of microns to couple of millimeters, prevent an anode substrate and a cathode substrate in a vacuum state from being collapsed by the outside atmospheric pressure, and thereby the spacers play a role of preventing a cross-talk that is a mutual interference phenomenon between pixels in the operation process of elements.
Requirements of said spacers are as follows: That is, they should not be seen visually (50˜100 μm in their width, 25:1 or more in their aspect ratio), and they should have physical and chemical durability (required strength for the FED: 14.7 lbs/inch2=1.0 lbs/2.1 inch-diagonal). Moreover, upper and lower substrates should match in the coefficient of thermal expansion and so forth in order to prevent damages by the stress in a thermal process. In addition, their gas separation phenomenon and reactivity on florescent substance should be low. Also, they should have surface conductivity as long as insulation between cathode and anode electrodes is maintained such that electric charge accumulation is prevented, and a production level of secondary electrons should be low in order to prevent electric breakdown.
The above spacers are formed using frit, polyimide, glass structures (cross, pillars, rib, ball, and so forth), ceramic structures, optic fibers, and etc. Above all, glass structures and optic fibers are mainly used in forming the spacers.